This invention relates to an improved double filtering filter for lubricating oil or lubricant of internal combustion engines of motor vehicles.
Italian Patent No. 1 141 751 discloses a double filtering filter of the type to be screwed, comprising a rough filter cartridge and a fine filter cartridge superimposed together, contained in a cylindrical housing closed by a cover, equipped with a central hole for the lubricating oil undergoing the rough filtering, and an eccentric hole for draining into the oil sump the lubricant undergoing the fine filtering, as well as inlet holes for the lubricant to be filtered.
In the commercial construction of this known filter, the fine filtering cartridge is made up by cotton flock compressed in a box of punched plate shaped as a cylindrical hollow body or sleeve. Therefore, the manufacturing of such cartridge requires the forging of two strips of punched plate forming the inner and outer cylindrical surfaces of the box, their curving as a ring and the folded seam of the opposed ends, and thereafter the fitting of plate disks with central holes as a lower and an upper base of the cartridge, after the filling of the pressed cotton.
This construction results to be expensive due to the installations required for the operation and to the necessary labor.